A Brief Study on Piezo Actuators and their Feasibility as a Tactile Communication Device

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A Brief Study on Piezo Actuatorsand their
Feasibility as aTactile Communication Device

• Abhishek K. Agarwal
• Department of Electrical and Computer Engineering
• University of Illinois at Urbana-Champaign
• Beckman Institute for Advanced Science and
  Technology
• BioMEMS Group
• 27 April 2000

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DISCUSSION

• Introduction
• MEMS Technology
• Potential use of oral tactile communication
  devices
• Piezoelectric Materials
• Background
• Utilization in project

• Experimental setup
• Driving Piezo film
• Mouthpiece fabrication
• Testing
• Results
• Concerns
• Closing Remarks

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INTRODUCTION

• MEMS Technology
• Recent surge
• Versatile field with enormous applications
• Ink-jet printers
• Accelerometers
• CMOS / MEMS Integration
• Mirror alignment
• Microengines

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INTRODUCTION

• Potential as an oral tactile communication device
• Advances in nano-fabrication processes
• Strong motivation
• New research
• New mode of communication
• Auditory and visual

• External vibrotactile devices
• Large and consume much power
• Desire to investigate possibility of mouth-based
  interface
• Mouth is one of most sensitive parts of body
• Military applications
• Device for disabled

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INTRODUCTION

• Why tactile?
• Auditory / visual aids already available
• Help reduce sensory overload
• Keep individuals visual/auditory and hands free
• Military scenarios
• Less susceptible to disorientation
• Directly channeled mode

• Tactile devices
• Electrotactile
• Direct stimulation of nerve/receptor
• Vibrotactile
• Electromagnetic transducers
• Piezoelectric materials (ceramics and PVDF)

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PIEZOELECTRIC MATERIALS

• Jacques Pierre Curie
• Discover Piezoelectric phenomenon in 1880
• Mechanical stress induces electric field
• Lippmann (theoretically) derives converse in 1881
• Curies (experimentally) confirm existence
  thereafter

• Material is Piezoelectric
• If mechanical stress induces an internal
  dielectric displacement, thereby creating an
  external surface charge
• If imposed external surface charge/electric field
  induces a mechanical stress (the converse)

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PIEZOELECTRIC MATERIALS

• Why does the phenomena exist?
• Some atomic lattice structures have as an
  essential unit (or cell) a cubic or rhomboid
  cage made of atoms. This cage holds a single
  semi-mobile ion which has several stable quantum
  position states inside cell. The ion's post-ion
  state can be caused to shift by either deforming
  cage (applied strain) or by applying an E-field.
  The coupling between the central ion and the cage
  provides the basis for transformation of
  mechanical strain to internal E-field shifts, and
  vice versa.

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PIEZOELECTRIC MATERIALS

• Mechanical Stress
• Pressure on electrically neutral crystals
  polarizes them by slightly separating center of
  positive charge from that of negative charge
• Results in development of measurable E-field

• Electrical Stress
• Alternating electric fields produce alternating
  mechanical vibrations of same frequency
• Cantilever Motion

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PIEZOELECTRIC MATERIALS

• Project Specifications
• Stainless steel bending shim
• Exhibits Cantilever motion
• 0.7 ? 0.04 ? 0.02
• Parallel poled
• Actuator with voltage applied across each ceramic
  layer individually (3 layer device)

• How to access device?
• Make contacts as shown below
• Center shim must be accessed for deflection

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EXPERIMENTAL SETUP

• Driving circuit
• Pulsed voltage needed to actuate bender
• Methods
• Design DC power source from 15V source and use
  amplifier circuit to create pulsed voltage
• Simple amplifier circuit and DC power source

• PSpice
• Simulations done before design of physical
  circuit below

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EXPERIMENTAL SETUP

• How to obtain maximum deflection
• Characterization of Actuator
• Variables considered
• Input DC voltage (100-300 V)
• Input current from DC power supply (0-4 mA)
• Input frequency from HP Func. Gen. (1-150 Hz)

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EXPERIMENTAL SETUP
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EXPERIMENTAL SETUP

• Concerns
• Electrical hazard
• Insulator Properties
• Easily applicable (uniform coating)
• Biologically safe (non-toxic)
• Minimal deterrence of deflection
• No alteration of physical properties of Piezo
  strip

• Not prone to breakdown from mouth environment
• Most important high dielectric properties
• Possible Solutions?
• ResTech Biwax 9700
• Polyimide 2611
• Shrink tubing
• Electrical tape

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EXPERIMENTAL SETUP

• Coatings
• Non-uniform coatings
• Tedious application procedures
• Medium durability

• Other solutions
• Shrink tubing and electrical tape hindered
  deflection
• Final Answer
• 3M Adhesive tape
• Only 7-8 mils thick
• Excellent dielectric properties

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MOUTHPIECE FABRICATION

• Device to hold Piezo strip inside mouth
• Retainer-like device
• Requirements
• Small and very versatile to allow full movement
• Provides linear and rotational motion in mouth
  for easy placement
• Does not promote electrical hazard
• Comfortable for user

• Possibilities
• Sport mouthguard
• Various dental impression compounds
• Kerr Impression (Type I)
• Cuttersil Putty Plus (Silicone Impression)
• SuperGel (Alginate Impression Powder)

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MOUTHPIECE FABRICATION

• Physical design
• PVC material
• Extreme versatility considered
• Two-part concept
• Mouthpiece / Track
• Piezo strip holder

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MOUTHPIECE FABRICATION
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TESTING INSIDE MOUTH

• First Safety concerns
• Shock hazards
• 3M Adhesive tape
• Resistors to limit current
• Non-conductive epoxy at solder joints
• Shrink tubing around wires
• Discussion with co-workers

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TESTING INSIDE MOUTH

• Results
• None (at the moment) a few more checks needed
  of entire setup before beginning any testing
• Methods
• Tangential sweep across surface of mouth
• Less stimulation/force required
• Tapping force (perpendicular to mouth surface)

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FUTURE WORK

• Map upper-roof of mouth
• Obtain sensitivity data
• Determine difference between tangential and
  perpendicular contact
• More versatile mouthpiece
• Fit Piezo strips into a sheath that will
  conform to roof of mouth

• Other interests
• Extension to a two-way communication device
• Fabrication of piezoceramic devices in polyimide
  base
• Wireless system
• Possibility of creating required power?
• Circuitry inside mouth?

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CLOSING REMARKS

• Piezoelectric phenomena
• Multitude of applications
• Feasibility of use as an oral tactile
  communication device?
• Possible device is simple and easy to feel

• Major complication
• Large power needed for deflection
• Many opportunities for further study

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ACKNOWLEDGEMENTS

• BioMEMS Group
• Professor David Beebe
• Hui Tang
• Beckman / ECE Machine Shop